Freshly poured concrete usually requires leveling or grading with a screed or rod to provide a smooth surface at a desired level or grade. Tamping is also usually advisable to eliminate internal voids in the wet concrete. These operations are usually followed by floating and finishing to further refine the surface.
Conventional screeds have a blade long enough to span the entire concrete slab and are operated by a minimum of two persons who are stationed at opposite sides of the slab. The two operators synchronously travel their ends of the screed along the slab. One or more additional persons are required to scrape away excess material which accumulates in front of the advancing screed. Some more complex and costly screeds are motor driven but the duplication of effort is still essentially present as drive mechanism must be provided at both sides of the slab. It would be advantageous to reduce the number of personnel and/or complication of the mechanism that is required for such purposes.
A conventional screed of sufficient length to span large area slabs, such as building floors for example, becomes cumbersome and awkward if it must also be used on small area slabs or small extensions of a large slab. The screed may overlap such slabs for a substantial distance. The problem becomes particularly acute if there are obstacles or terrain variations in the vicinity of the slab. Use of an oversized screed may be difficult or impossible if there are upslopes, downslopes, trenches, walls, or piles of construction materials adjacent the slab.
Mismatch of the conventional screed with the slab area to be leveled can occur temporarily at certain stages only of a single operation if the area is angled or non-rectangular. The screed must, for example, temporarily span a greater distance while being turned at an angle in a slab than while being travelled along other portions of the slab. Slabs may also have extensions that are of less width than the main body of the slab. The effective working area of such a screed on a circular slab progresses from a minimum to a maximum and then back to the minimum.
Problems arising from excessive overhang of screeds with the work area can be alleviated to some extent under some conditions if a number of screeds of differing length are available. This is not always an effective solution, particularly on angled or non-rectangular slabs as discussed above, and at best requires a bulky and costly duplication of equipment.
Providing a number of screeds of different sizes is particularly disadvantageous in the case of vibrating screeds which include costly mechanism for accomplishing tamping concurrently with the leveling or grading operation. Transportation of a number of such mechanisms to and from a job site also adds significantly to costs.
The present invention is directed to overcoming one or more of the problems discussed above.